1. Field of the Invention
The present invention relates to an electroconductive sliding apparatus for electrically connecting two relatively moving electroconductive members, and more particularly to an apparatus for grounding static electricity developed on the surface of a disk for a magnetic disk apparatus and the like.
2. Description of the Prior Art
Conventional apparatuses of this type are typified by the following three examples. The first example involves an apparatus using a sliding member as shown in FIG. 22 (refer to Japanese Laid-open Utility Model, Application No. 126,495/1986).
The apparatus is composed of an electroconductive sliding member 3 energized on the side of a shaft 1, by means of a spring plate 2, between an electroconductive shaft (first member) and an electroconductive spring plate (second member), the shaft 1 being electrically connected to the spring plate 2 by means of the sliding member 3. The sliding member 3 is integrally formed on the spring plate 2 prepared by blending a solid lubricator with the surface coated with nickel, carbon fiber and a synthetic resin in a definite proportion.
The second example (not shown) includes an apparatus using a mercury slip ring between two relatively moving electromotive members.
The third example includes an electroconductive sliding apparatus used for a magnetic disc apparatus disclosed in U.S. Pat. No. 4,604,229. The apparatus is, as shown in FIG. 23, composed of an electroconductive magnetic fluid 8 interposed between a magnetic shaft (first member) 4 and a magnetic pole piece (second member) 7 immovably attached, on both sides of a magnet 6, to the internal periphery of a non-magnetic, electroconductive housing 5, thereby sealing between the shaft 4 and the pole piece 7 and electrically connecting the shaft to the piece.
In the first example (FIG. 22), the electroconductive sliding member 3 which is brought into direct, resilient contact with the shaft 1 is electrically connected to the shaft 1 and plate 2 but lacks lubricativity even when it contains solid lubricant. Accordingly, rotation of the shaft 1 may, with time, cause abrasion of the sliding member and increased or uneven torque, thus finally causing vibration and noise. For the same reason, the shaft 1 which rotates at a high speed may cause heat and adverse effect on the apparatus.
In the second example (not shown), the slip ring using mercury, the two electroconductive members can be electrically connected by mercury, and lubrication is also possible therebetween. However, mercury, fluid and volatile, makes the sealing mechanism complex and the apparatus expensive. The toxicity of mercury makes apparatus handling difficult.
In the third example (FIG. 23), lubrication between the shaft 4 and the pole piece 7 is performed effectively, but the electroconductivity is quite high, because the gap distance is usually about 200 .mu.m, so that the layer of the electroconductive, magnetic fluid 8 therebetween is quite thick. The experimental value of the electroconductance was from 10.sup.7 to 10.sup.8 ohms and was nearly ineffective for removing the static electricity of the disk mounted on the shaft 4. Although U.S. Pat. No. 4,604,229 describes that a magnetic fluid with an electroconductance of several kilohms is manufacturable; the fluid increases contact torque due to increased viscosity with decreased resistance. When torque in a practical level is to be realized, the value of the resistance of the magnetic fluid will be as great as several megohms. Grounding of static electricity will require that the resistance between the shaft 4 and the pole piece be as low as several kilohms or less. In view of this fact, electrical connection therebetween would not be satisfactory.